1. Field of the Invention
The present invention relates in general to a television receiver which is capable of processing a quadrature-modulated composite video signal, and more particularly to a luminance/color signal separation apparatus which is capable of suppressing a cross luminance phenomenon and a cross color phenomenon which are liable to occur when luminance and color signals are separated from a composite video signal, a correlation of which is high all vertically, horizontally and diagonally, is vertically low and horizontally high or is vertically high and horizontally low.
2. Description of the Prior Art
Generally, in order to efficiently use a frequency band in a quadrature modulation broadcasting system such as, for example, a NTSC broadcasting system, a composite video signal is transmitted to a television receiver, with a color signal interleaved in a luminance signal. In the television receiver, the luminance and color signals must perfectly be separated from the composite video signal. In this case, a cross luminance phenomenon of the luminance signal and a cross color phenomenon of the color signal may take place when the luminance and color signals are not perfectly separated from the composite video signal.
In one conventional apparatus for separating the luminance and color signals from the composite video signal using linear filters, the color signal is detected from the composite video signal utilizing a band pass filter and a low pass filter. In this case, a color subcarrier is employed as center frequencies of the band pass filter and the low pass filter.
In another apparatus for separating the luminance and color signals from the composite video signal using the linear filters, the color signal is detected from the composite video signal utilizing a characteristic that the color signal is inverted in phase every line and every frame in the case where the composite video signal belongs to the quadrature modulation broadcasting system. In this case, the color signal is detected from the composite video signal on the basis of an arithmetic operation of line and frame comb filters which can be expressed by the following equation: EQU 1/2P1-1/4(P0-P2)
where, P0 is the composite video signal inputted by the apparatus, P1 is a composite video signal which is obtained by delaying the composite video signal P0 by one line using the line comb filter and P2 is a composite video signal which is obtained by delaying the composite video signal P1 by one line using the line comb filter.
In a further apparatus for separating the luminance and color signals from the composite video signal using the linear filters, the color signal is detected from the composite video signal utilizing a series connected band pass filter and line or frame comb filter in consideration of a resolution of the luminance signal.
In yet another apparatus for separating the luminance and color signals from the composite video signal using the linear filters, the color signal is detected from the composite video signal utilizing a low pass filter and a line or frame comb filter depending on motion of the composite video signal. In this case, the color signal is detected from the composite video signal on the basis of an arithmetic operation of the line or frame comb filter which can be expressed by the following equation: EQU 1/2P1+1/4(P0+P2)
where, P0 is the composite video signal inputted by the apparatus, P1 is a composite video signal which is obtained by delaying the composite video signal P0 by one line using the line comb filter and P2 is a composite video signal which is obtained by delaying the composite video signal P1 by one line using the line comb filter.
In one of conventional apparatus for separating the luminance and color signals from the composite video signal using non-linear filters, the color signal is detected from the composite video signal utilizing a logical comb filter which is shown in "IEEE 1985 Consumer electronic Vol. 31 No. 3 pp 240-254", SONY. In this case, the color signal is detected from the composite video signal on the basis of an arithmetic operation of the logical comb filter which can be expressed by the following equation: EQU Max{Min(P0,-P1), Min(-P1, P2)}+Min{Max(P0,-P1), Max(-P1, P2)} or EQU Max{Min(-P0, P1, P2), 0}+Min{Max(-P0, P1, P2), 0}
where, P0 is the composite video signal inputted by the apparatus, P1 is a composite video signal which is obtained by delaying the composite video signal P0 by one line and P2 is a composite video signal which is obtained by delaying the composite video signal P1 by one line.
The luminance signal is detected by removing the color signal detected on the basis of the above arithmetic operation from the inputted composite video signal.
However, in the above-mentioned conventional apparatus for separating the luminance and color signals from the composite video signal using the linear filters, the luminance/color signal separation apparatus employing the band pass filter and the low pass filter has a disadvantage in that horizontal resolution is reduced because a cross luminance phenomenon of the luminance signal such as a dot crawling phenomenon and a cross color phenomenon of the color signal such as a rainbow pattern color spread phenomenon may take place when the composite video signal has a horizontal or diagonal variation.
Also, the luminance/color signal separation apparatus employing the line comb filter has a disadvantage in that a vertical resolution is reduced because a cross luminance phenomenon of the luminance signal such as a dot hanging phenomenon and a cross color phenomenon of the color signal may take place when the composite video signal has a vertical or diagonal variation.
Further, the luminance/color signal separation apparatus employing the frame comb filter has a disadvantage in that a cross-talk phenomenon occurs between the luminance and color signals since the luminance and color signals are not perfectly separated when the composite video signal has a variation in time.
On the other hand, the above-mentioned conventional apparatus for separating the luminance and color signals from the composite video signal using the non-linear filters has a disadvantage in that the luminance and color signals are not perfectly separated when the composite video signal has the horizontal or diagonal variation. Also, the luminance signal cannot directly be obtained.